As in other programming languages, variables are used to store data of different values or types (hence the name variable). In Python, you declare a variable by writing its name and then assigning its value with the equal (=) sign:
my_variable = 4When naming variables, there are a few rules to keep in mind:
Variable names must start with a letter or an underscore (_), but not a number.
They can only contain letters, numbers, and underscores.
Names are case-sensitive (
my_Variableandmy_variableare different).It’s a good practice to use descriptive names and follow the snake_case convention (e.g., my_variable).
Notice that when we initialize a variable, we do not need to specify its type (e.g. it being an integer or a string), as Python is dynamically typed, which means it figures out your desired variable type by itself once you run the program. This means, you can also simply overwrite your previously created variable with for example a character string:
my_variable = "Hello World"If you want to know what’s currently stored in your variable, you can use the print() function:
print(my_variable)Hello World
Note: If you are working in an interactive environment like the Jupyter notebooks which we will use in the exercises, you might not even need to write print as the last line of the code cell is automatically evaluated.